Method of forming silver sulfide coatings



Patented July 27, 1948 Clifiord W. Mell, Moorestown, N. J., assignor to Radio Corporation of America, a corporation of Delaware NorDrawingr Application August 24, 1944, Serial N0."551,063

This invention relates to the method of forming silver sulphide coatings on'articles having a silver surface, and more particularly to the formation of a uniform, black silver sulphide deposit upon solid silver or silver plate.

There are certain applications wherea, uniform deposit of silver sulphide upon silver or silver plate is very desirable. For example, in the case of certain types of electrical apparatus employing silver or silver surfacedconductors through which high frequency currents are passed, it has been found advantageous to provide on such conductors a surface layer of silver sulphide for the purpose of controlling such currents in desired manner. In

such cases, it is quite essential that the surface deposit or layer of silver sulphide be even and uniform. The production of an even, uniform deposit of silver sulphide on silver has usually been found to bevery difiicult, if not even impossible,

according to prior art methods. r

The primary object of my present invention is y to provide an improved method offorming a coating or deposit of silver sulphide upon articles having silver surfaces, which method willnotbe subject to the limitation of conventional, prior art methods.

More particularly, it is an object ofthe present invention to provide an improved method of form- Claims. (or. fitam) ing auniform, evenfilm or deposit ofsilver suli phide on solid silver or on silver plate regardless of what the silver may be deposited upon in the latter case.

Another object of my present invention is to provide an improved method of forming silver sulphide deposits on silver as aforesaid which can be very easily and accurately controlled between Wide limits for the purpose of varying the color and density of the deposit.

Still another object of my present inve'ntionis to provide an improved method of forming silver sulphide deposits on silver whereby black deposits of silver sulphide can be applied quickly and easily, the resulting deposits not being harmful to the silver and affecting it only by turning the surface thereof black.

A further object of my present invention is to provide an improved method of forming silver sulphide coatings as aforesaid which will not require complicated equipment such as has been required by prior art methods and which is very inexpensive to carry out in practice.

Still a further object of my present invention is to provide an improved method of forming deposits of silver sulphide on silver surfaces which can be readily practiced even by one. not skilled inthe'art; a a

Itfislalso anobject of mypresent inventionto provide an improved method of forming silver sulphide deposits or coatings on silver which is highly efficient in useg V v i In accordance with my present invention, the article having a, silver surf ace is, first, treated with a ,wa'tersolution or water emulsion of a filmforming hydrophilic substance to which may be added a wetting agent. The film-forming hydrophilic, substance may be a water soluble wax-like derivative of a polyhydric alcohol, or,a film- -forming hydrophilic colloid. Thisforrns alfilm on the surface of the silver. The water present in the film is; allowed to evaporate, and, when the nlm is dry, thetreated article is placedlin an atmosphere containing from about percent to percent humidity and a suitable concentration of free hydrogen sulphide. The operation may be performed at room temperature; The speed of formation of the film is increased by increase in humidity, temperature, concentration of'the hydrogen sulphide and the time of exposure. The

silver sulphide deposits which are formed are an integralpart of the surface and cannot be rubbed off easily;

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The'invention it- 'self, howeverftogether with additionalflobjects and advantages thereof, will best, be understood from the" (following[description of one embodimentthereof: v

v A solution oremulsion is ,prepared byi dispersing afilm-forming water soluble, wax-likederivative of polyhydricalcohols, or ,afilm-forming hydrophilic colloid in water with the aid ofa .wetting agent. theWaX-Jike derivatives of polyhydric alcohol which lhave found satisfactory is one sold under the trade name Carbowax 4000. This is a hard, translucent solid composed of polyethylene glycols having an average molecular weight of around 4000 and a meltin point of from about 50 C. to about 55 C. Gelatine, agar, etc., may be mentioned as representative of film-forming hydrophilic colloids which are suitable for use according to my present invention. Any one of a number of well known Wetting agents, such as triethanolamine, Triton NE Special (a non-ionic wetting agent consisting of an alkylated phenoxy polyethoxy ethanol in which the alkylating groups may contain from 5 to 16 carbon atoms), or the like may also beused, if desired. A typical formula which is representative but which is not to be taken as limiting, since the particular ingredients may be varied and since various concentrations thereof may be employed, is as follows:

Parts Carbowax 4000 Triton NE Special 2 Triethanolamine 2 Water 100 A typical, representative formula employing one of the film-forming hydrophilic colloids is the following:

a humid atmosphere saturated with hydogen sulphide and containing from about 90 percent to about 100 percent humidity until a desired coata Parts- Gelatine 5 Triton NE Special i 2 Triethanolamine 2 Water :100:

in solution or in an emulsion. The silverware or silver surfaced article on which the silver sulphide deposit is'to be formed is treatedwith this solution or emulsion, as by dipping, spraying, or the like; to form a film of the solution or the emulsion thereon, as the case may be. The excess liquid is allowed to drain ofi from the article and the water in the film is permitted to evaporate until the'surface is air dried. The treated silver article is then hung or otherwise suitably placed in an enclosure in which is present from about 90 percent to about 100 percent humidity and suflicient hydrogen sulphide to cause blackening. A very easy and satisfactory method of accomplishing this atmosphere is to place in the enclosure an open jar (preferably of glass) containing about 500 ml, of water for every cubic foot of air present in the enclosure, the. water being saturated with hydrogen sulphide. The humid hydrogen sulphide fumes emanating from the hydrogen sulphide solution'will react chemically with the silver sulphide surface to produce a firm, adherent,

uniform, even silver sulphide deposit thereon.

The reaction may be carried out at room temperatures, that is,,between approximately 70 F. and 90 the higher the temperature, the more speedy being the reaction. The density of the deposit'of silver sulphide and the blackness of the color thereof which is desired determine'the'time of exposurawhich may'vary from about one hour to several hours.

Fromthe foregoing description, it will be apparent to those skilled'in the art that I'have provided' a novel 'and'simple, yet highly effective method of providing a uniform, adherent coating 'ing of silver sulphide has formed on said treated surface.

2. Th method of forming a coating of silver sulphide ona silver surface which comprises first treating said silver surface with a solution of a water soluble wax-like derivative of a polyhydric alcohol, then drying said treated surface, and then exposing said treated surface to a humid atmosphere saturated with hydrogen sulphide and containing from about 90 percent to about 100 percenthumidity until a desired coatingof silver sulphide has formed on said treated surface.

3. The method of forming a coating of silver sulphide on a silver surface which comprise first treating said silver surface with a water emulsion of a film-forming hydrophilic colloid, then drying said treated surface, and then exposing said treated surface to a humid atmosphere saturated with hydrogen sulphide and containing from about 90 percent to about 100 percent humidity until a desired coating of silver sulphide has formed on said treated surface.

4. The method of forming a coating of silver sulphide on an article having a silver surface which comprises first treating said silversurface with a water emulsion of a film-forming hydrophilic substance, then drying the treatedsurface, and then placing said article in an enclosure containing a solution of approximately 500 ml.'.of water for every cubic foot of air in said enclosure and saturated with hydrogen sulphide whereby to subject said treated surface to humid hydrogen sulphide fumes emanating from said solution, and retaining said article in said enclosure'until a desired coating of silver sulphide has formed on said surface.

5. The invention set forth in claim' wherein the-contents of said enclosure are maintained at temperatures of between about F.'and F].

V I CLIFFORD W. MEIL.

REFERENCES CITED The following references are of record in the file of thispatent: V

' UNITED STATES PATENTS Number Name Date 2,079,690 Grisdale May 11, 1937 2,339,200 Sowa Jan. 11, 1944 

